This invention relates to a method and apparatus for producing a hot fluid stream from which power can be recovered.
It is known to generate power from a fuel gas by compressing the fuel gas, burning it in a combustion chamber employing compressed air to support combustion, and expanding the products of combustion in a turbine. The turbine is used to drive an alternator and hence generate electrical power. Known sources of suitable fuel gas include reactors in which the direct reduction of iron oxide to form iron and/or the gasification of coal are performed. In these examples, the fuel gas is produced at an elevated temperature and is laden with particulates. The fuel gas is scrubbed to remove the particulates and is cooled to ambient temperature.
Frequently, the process producing the fuel gas requires a supply of commercially pure oxygen or oxygen-enriched air. The oxygen or oxygen-enriched air is frequently produced by a plant that operates on the same site as the reactor in which the fuel gas is produced. Nitrogen is produced by the plant in addition to oxygen.
There are a number of proposals in the art for recovering work from the nitrogen. In some proposals, the nitrogen is compressed and then passed to the gas turbine in which the fuel gas combustion products are expanded. The nitrogen may be passed directly into the expansion turbine or into a region upstream thereof. By this means, most if not all of the energy requirements of the air separation can be met. Examples of such methods are included in U.S. Pat. Nos. 2,520,862 and 3,771,495.
It has also been proposed in our European patent application EP-A-402 045 to recover work from nitrogen by heat exchanging it at elevated pressure with a hot gas stream and then expanding the resulting warmed nitrogen with the performance of external work.
None of the prior processes discussed above provides a means for making use of the elevated temperature of the fuel gas in the generation of power.